"As a competitor and as someone who's really passionate about their work, I got a little overexcited," Williams told "Good Morning America" today.

Play

null

Williams' tirade was ignited when the judge ruled that her foot crossed the line during a serve, resulting in a double fault.

"I feel like taking this [expletive] ball and shoving it down your [expletive] throat," Williams shouted while pointing her finger and walking toward the line judge, following up with more expletives.

Williams was fined $10,000 for the Sunday rant and penalized the final point in her semifinal match against Kim Clijsters. Tournament officials are investigating whether more punishment should follow.

"At that point, I had really just lost control," she said, noting that the call was over a mistake she hadn't made all year. "I just thought, 'What's going on?'"

Williams said she especially felt sorry for the judge who was obviously taken aback by Williams' harsh words and aggressive stance.

"I felt like I wanted to give her a big hug, obviously after the whole tirade was over," she said. "And tell her, you know, 'I'm sorry.'"

The incident, Williams said, was just another lesson learned on the court that she will take with her.

Her new book, "On the Line," discusses Williams' ups and downs not only on the court but throughout her life as she rose from the courts of Compton, Calif., to peak as the world's top-ranked female tennis player.

But after undergoing surgery and the shocking murder of her sister Yetunde Price in 2003, Williams said she began to struggle. Her ranking dropped and "everything came crashing down," she said.

"It was really hard to go through that," Williams said, tearing up as she talked about her sister being part of the motivation to share her story.

Serena Williams Repents

But Williams, who won her first grand slam title at age 17 before going on to collect 22 more, rebounded.

"Everyone has downs," she said. "Everyone can learn from them."

In the book, Williams told about the messages she writes herself, including lines such as "Play angry, but let them see confidence. Play angry, but let them see patience."

And, now, as she faces possible additional punishment for her U.S. Open outburst, Williams said she may have to add a new chapter.

"I love my fans. I love the kids. I feel honored to have people look at me and be like, 'I want to be Serena Williams,'" she said, adding that she never expected to be in such a position. "It's greater than the sport."

And that's why, she said, she apologized, backing away from her initial statement shortly after the match that seemed unapologetic as she asked, "Well, how many people yell at lines people?"

This morning, Williams said, "I'm not perfect. I'm human. And no human is perfect except for Jesus. At the end of the day, I have to be responsible for my actions."

"I want to amend my press statement of yesterday, and want to make it clear as possible," the statement said. "I want to sincerely apologize FIRST to the lines woman, Kim Clijsters, the USTA, and tennis fans everywhere for my inappropriate conduct.

"I need to make it clear to all young people that I handled myself inappropriately and it's not the way to act -- win or lose, good call or bad call in any sport, in any manner."

Williams has taken in nearly $4.5 million in prize money in 2009 and is, at age 27, the No 2. woman player in the world, according to ESPN.